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What happens to Oregon’s tidal wetlands
with sea level rise?
This presentation summarizes the
MidCoast Watersheds Council’s
project on the impacts of SLR on
tidal wetlands in Oregon. Please
see the project report for details:
www.midcoastwatersheds.orgPhoto by David Pitkin
Project maps future tidal wetlands (6 SLR scenarios, 23 estuaries), predicts losses, prioritizes areas for focus
A project of the MidCoast Watersheds Council With funding from: Oregon Watershed
Enhancement Board & USFWS Coastal Program
Contractor: Estuary Technical Group
(Laura Brophy, Michael Ewald)
Project Manager: Fran Recht, PSMFC
Analysis covers 23 estuaries
south of the Columbia River
Necanicum River
Nehalem River
Tillamook Bay
Netarts Bay
Sand Lake
Nestucca Bay
Salmon River
Siletz Bay
Yaquina Bay
Alsea Bay
Beaver Creek
Yachats River
Siuslaw River
Umpqua River
Coos Bay
Coquille River
New River
Sixes River
Elk River
Rogue River
Pistol River
Chetco River
Winchuck River
Photo by David Pitkin
Our project maps tidal wetlands(wetlands that are flooded by the tides at least
once a year, usually daily to monthly)
This includes tidal marsh and tidal swamp, but not mud flats
Shrub
tidal
swamp
Forested tidal swamp
Tidal marsh
Why should we care about loss of tidal wetlands with sea level rise?
Tidal wetlands support many creatures
Salmon
Birds
Mammals
Other fish
& shellfish
What else can tidal wetlands do for us?
Store carbon in the soil, helping to reduce
global warming
Filter and clean water
Reduce flooding
Provide scenic beauty and recreation
Current Conditions:Yaquina Estuary –normal high tide
Current conditions, Yaquina Estuary “King Tide”…
Is this the future normal high tide?
If so, can our tidal wetlands survive into the future?
They can’t survive a lot more inundation…
They’ll remain in place if elevations are appropriate- otherwise move upslope- if they can
• Tidal wetlands may “keep pace” with sea level rise, if
there’s enough accretion (deposited sediment and
organic matter).
• If not, then tidal wetland vegetation won’t survive in
its current location, and wetlands will need to
“migrate” upslope (seed dispersal or roots).• We call the area they’ll move to, the “Landward
Migration Zone” or “LMZ”.
Tidal wetlands form in a narrow elevation range
This is the
Landward Migration
Zone or “LMZ”
In Oregon's estuaries much of the land bordering our marshes goes pretty quickly upslope, limiting the area available for LMZ
Elevation-based mapping - example
Tillamook estuary
tidal floodplain –
12 miles upstream
Our project depends on accurate elevation mapping (LIDAR) as well as NOAA hydrologic modelling to know where current tidal wetlands are (or would be without diking, i.e. the lands are at the appropriate elevation to support tidal wetlands if opened to the tides...)
Elevation-based mapping
Where are the
current and former
tidal wetlands?
Elevation based mapping
This low ground just
above current tide range
is the “Landward
Migration Zone” or “LMZ”:
Potential future tidal
wetland
Current areas
within tidal wetland
elevation range
(blue & green)
Source of
projected
sea level
rise data:
National
Academy of
Sciences
2012 West
Coast SLR
study
SLR
scenarios
For Newport,
high end
of 2030 range
= 9” (23 cm)
High end
of 2050 range
= 1.6 ft (48 cm)
High end
of 2100 range
= 4.7 ft (142 cm)
We also added
an intermediate
scenario:
2.5 ft (75 cm)
and two higher
scenarios: 8.2
and 11.5 ft
(~2130, 2160)
Wetlands are shifting
into the “LMZ”
Many diked ag
lands (former
tidal marsh) are
water or mudflat
at 4.7 ft SLR
0
200
400
600
800
1000
1200
1400
0.0 0.8 1.6 2.5 4.7 8.2 11.5
LMZ
area
(ac)
SLR (ft)
Alsea Bay Estuary
Impervious
Not impervious
Potential tidal wetland acreage at each SLR scenario
Orange means
developed
(impervious)
areas.
Green color
shows areas that
are not
developed -- better potential
for future tidal
wetlands.
current
0
1000
2000
3000
4000
5000
6000
7000
0.0 0.8 1.6 2.5 4.7 8.2 11.5
LMZ
area
(ac)
SLR (ft)
Tillamook Bay Estuary
Impervious
Not impervious
Followed by sharp
decreases in tidal wetland
area when SLR is >2.5 ft
Most estuaries show a
pattern of slightly increased
tidal wetland area during
early SLR scenarios….
Results summed across all estuaries
Summed across all 23
estuaries, the model shows little
change in potential tidal wetland
area until >2.5 ft SLR…
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0.0 0.8 1.6 2.5 4.7 8.2 11.5
LMZ
area
(ac)
SLR (ft)
All 23 estuaries
Impervious
Not impervious
But potential tidal
wetland area
drops sharply
with SLR >2.5 ft:
-21% at 4.7 ft
-41% at 8.2 ft
-60% at 11.5 ft
LMZs are not in the same places as current
tidal wetlands
• Bar charts don’t show how the locations of future tidal
wetlands differ from current tidal wetlands
• At 4.7 ft SLR, 2/3 of potential tidal wetlands are in different
places from current tidal wetlands
• At 8.2 and 11.5 ft SLR, there is no overlap between
locations of future and current tidal wetlands.
Summary of results
• Most estuaries show a sharp decline in potential tidal
wetland area after 2.5 to 4.7 ft SLR
• Although some estuaries show LMZ gains, these tend to be
small in acreage
• Maps show locations of LMZs, for action planning
• Maintaining tidal wetland functions will require landscape-
scale thinking
– At 4.7 ft SLR, 2/3 of potential tidal wetlands are in different locations
from current tidal wetlands
• The landscape is big; funds are small
• Are all LMZ areas of equal value to conserve?• Prioritization of areas will help groups with
their action planning
So... What should we do?
We scored LMZs using 5 factors that affect importance
and feasibility of conserving & restoring LMZs.
• Future tidal wetland area (hectares) at 4.7 ft SLR
(more = higher score)
• Area of even higher LMZs (8.2 and 11.5 ft SLR)
• Current land use zoning (non-developed = higher)
• Land ownership (public = higher)
• Development status (undeveloped = higher)
Setting priorities: some criteria
We added the
5 scores to
calculate a
total score
Nestucca River estuary
Black areas
indicate
developed
(impervious)
land
This scoring & underlying data may help local groups make decisions about areas for focus
Prioritization results
Tools we provide
For each estuary:
• Future tidal wetland maps and data for 6 SLR scenarios
• Maps, data of prioritization rankings
• Tables and bar charts of potential tidal wetland area –
now, and in the future
• Report describing potential ways to use the data, and the
limitations of the data
• “Plan for resilience” – look upslope and into the
future
• Use maps to understand vulnerability (e.g.
subsided lands)
• Help decide where to work – consider easements,
restoration activities, other tools to conserve LMZs
• Recognize that gradients and connectivity are
important, regardless of sea level rise
How can the results be used?
Questions?
Laura [email protected]
Estuary Technical Group
Institute for Applied Ecology,
Corvallis, OR
Fran [email protected]
Pacific States Marine Fisheries Commission, Habitat Program
• Accretion (and organic matter accumulation) can definitely
keep up with limited, historic SLR.
– Can they keep pace with rapid, accelerated SLR?
• This project did not use an accretion model…
– That’s why we have shown the year with a question
mark (e.g. 2050?)
– SLR will continue; date may vary but sea level will
ultimately reach the level shown
What about accretion rates?
Tectonics & different land uplift rates:
– Could lead to slightly different relative SLR rates
– Effect is smaller than the error in models
– Literature doesn’t support adjustments to LMZs based
on tectonics
What about land uplift rates / tectonics?
What about earthquakes?
A major subduction zone earthquake:
• Would have a huge effect on tidal wetland distribution across
the landscape
• Immediate post-seismic subsidence could be over a meter
• Accretion would gradually fill in the subsided area, as it did
after the 1700 earthquake
• Rate of recovery is unknown
